Nullable value types in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nullable value type in C#?

A nullable value type is a value type that can also hold a null value, allowing it to represent the absence of a value. It is declared using a question mark after the type, for example, int?.

beginner

How do you declare a nullable integer in C#?

You declare a nullable integer by adding a question mark after the type: int? myNumber;. This means myNumber can hold any integer or null.

intermediate

What does the HasValue property do in nullable types?

The HasValue property returns true if the nullable type contains a non-null value, and false if it is null.

intermediate

How can you safely get the value of a nullable type?

You can use the Value property if HasValue is true, or use the null-coalescing operator ?? to provide a default value, for example: int value = myNumber ?? 0;.

intermediate

What happens if you try to access the Value property of a nullable type that is null?

Accessing the Value property when the nullable type is null throws an InvalidOperationException. Always check HasValue before accessing Value.

How do you declare a nullable double in C#?

A double!

B nullable double

C double?

D double*

In C#, you declare a nullable value type by adding a question mark after the type, like double?.

What does int? x = null; mean?

A x is a string

B x is a nullable reference type

C x is a non-nullable integer

D x is an integer that can be null

The int? means x is a nullable integer, so it can hold an integer or null.

Which property tells if a nullable type has a value?

A IsEmpty

B HasValue

C Value

D IsNull

The HasValue property returns true if the nullable type contains a value.

What does the expression myInt ?? 10 do?

A Returns myInt if not null, otherwise 10

B Always returns 10

C Throws an error if myInt is null

D Returns null if myInt is null

The null-coalescing operator ?? returns the left value if it is not null, otherwise the right value.

What happens if you access Value on a null nullable type?

A Throws InvalidOperationException

B Returns 0

C Returns null

D Returns default value of the type

Accessing Value when the nullable type is null throws an InvalidOperationException.

Explain what nullable value types are and why they are useful in C#.

Think about how you might represent an empty or missing number.

Describe how to safely work with nullable value types to avoid exceptions.

Consider how to avoid errors when the value might be missing.